A data backup technique is an important means for protection and recovery of data when a failure occurs in a computing system. The backup technique actually implemented at each operating center is selected on the basis of several parameters, such as the extent of failure that can be handled, the discrepancy of data with the backup site, the interruption of applied work, and the amount of delay in the response time of the storage system.
Among these backup techniques, there is a backup technique called remote copy. This is a backup technique in which a storage system itself copies information having received write requests to another storage system. Here, the system as a source of copying is called the local system, and the system as a destination of copying is called the remote system. As an example of remote copy, the SYMMETRIX remote data function is explained in “New products: General-Purpose Parallel Processor and Disk Array”, Nikkei Watcher IBM version, Special Issue, ISBN 4-8222-1558-X, published by Nikkei Business Publications, Inc., Nov. 13, 1995, pp. 256-291.
Here, the path connecting the local system and the remote system can be a storage interface, such as ESCON (Enterprise System Connection) in the case of short distance transmission, but in the case of long distance transmission, it goes by way of a circuit using a director or switch. In the case of going through such a circuit, especially with a public circuit, encryption of remote copy data is frequently used as a countermeasure against unauthorized receipt of data. Such encryption and decryption is performed by the storage system itself, or by a director or switch, or the like.